Image guidance systems have been widely adopted in neurosurgery and have been proven to increase the accuracy and reduce the invasiveness of a wide range of surgical procedures. Currently, image guided surgical systems (“Navigation Systems”) are based on a series of images constructed from data gathered before the operation (for example by MRI or CT) which are registered in relation to the patient in the physical world by means of an optical tracking system. To do this, detecting markers are placed on the skin of the patient and they are correlated with their counterparts visible on the imaging data. During the surgical operation the images are displayed on a screen in 3 orthogonal planes through the image volume, while the surgeon holds a probe that is tracked by the tracking system. When the probe is introduced into the surgical field, the position of the probe tip is represented as an icon drawn on the images. By linking the preoperative imaging data with the actual surgical space, navigation systems provide the surgeon with valuable information about the exact localisation of a tool in relation to the surrounding structures and help to relate the intra-operative status to the pre-operative planning.
Despite these strengths, the current navigation systems suffer from various shortcomings.
Firstly, the surgeon needs to look at the computer monitor and away from the surgical scene during the navigation procedure. This tends to interrupt the surgical workflow and in practice often results in the operation being a two-people job, with the surgeon looking at the surgical scene through the microscope and his assistant looking at the monitor and prompting him.
Secondly, the interaction with the images during the surgery (e.g. switching between CT and MRI, changing the screen windows, activating markers or segmented structures from the planning phase, colour and contrast adjustments) requires the operation of a keyboard, a mouse or a touch screen, which is distracting for the surgeon and troublesome since the equipment needs to be packed with sterile drape. Although probe-type control devices have been proposed (see Hinckley K, Pausch R, Goble C J, Kassel N, F: A Survey of Design Issues in Spatial Input, Proceedings of ACM UIST'94 Symposium on User Interface Software & Technology, pp. 213-222; and Mackinlay J, Card S. Robertson G: Rapid Controlled Movement Through a Virtual 3D Workspace, Comp. Grap., 24 (4), 1990, 171-176), all have shortcomings in use.
Thirdly, a common problem to all current navigation systems which present imaging data as 2D orthogonal slices is the fact that the surgeon has to relate the spatial orientation of the image series including their mentally reconstructed 3D information to the orientation of the patient's head, which is covered during the operation.
A system that uses see-through augmentation by combining the naked eye view of the patient with the computer-generated images is currently under investigation (see Blackwell M, O'Toole R V, Morgan F, Gregor L: Performance and Accuracy experiments with 3D and 2D Image overlay systems. Proceedings of MRCAS 95, Baltimore, USA, 1995, pp 312-317; and DiGioia, Anthony M., Branislav Jaramaz, Robert V. O'Toole, David A. Simon, and Takeo Kanade. Medical Robotics And Computer Assisted Surgery In Orthopaedics. In Interactive Technology and the New Paradigm for Healthcare, ed. K. Morgan, R. M. Satava, H. B. Sieberg, R. Mattheus, and J. P. Christensen. 88-90. IOS Press, 1995). In this system, an inverted image on an upside-down monitor is overlaid over the surgical scene with a half-silvered mirror to combine the images. The user wears a head tracking system while looking onto the mirror and the patient beneath. However, the authors report significant inaccuracies between the virtual and the real object.
Other systems currently under research or development combine computer-generated images with the video of the surgical scene obtained through cameras placed at fixed positions in the operation theatre or a head mounted display of the user. The combined signal is then channelled into the HMD (“Head Mounted Display”) of a user. The three examples of such projects are disclosed at in Fuchs H, Mark A, Livingston, Ramesh Raskar, D'nardo Colucci, Kurtis Keller, Andrei State, Jessica R. Crawford, Paul Rademacher, Samuel H. Drake, and Anthony A. Meyer, MD. Augmented Reality Visualization for Laparoscopic Surgery. Proceedings of First International Conference on Medical Image Computing and Computer-Assisted Intervention (MICCAI '98), 11-13 Oct. 1998, Massachusetts Institute of Technology, Cambridge, Mass., USA; Fuchs H, State A, Pisano E D, Garrett W F, Gentaro Hirota, Mark A. Livingston, Mary C. Whitton, Pizer S M. (Towards) Performing Ultrasound-Guided Needle Biopsies from within a Head-Mounted Display. Proceedings of Visualization in Biomedical Computing 1996, (Hamburg, Germany, Sep. 22-25, 1996), pgs. 591-600; and State, Andrei, Mark A. Livingston, Gentaro Hirota, William F. Garrett, Mary C. Whitton, Henry Fuchs, and Etta D. Pisano (MD). Technologies for Augmented-Reality Systems: realizing Ultrasound-Guided Needle Biopsies. Proceedings of SIGGRAPH 96 (New Orleans, La., Aug. 4-9, 1996), in Computer Graphics Proceedings, Annual Conference Series 1996, ACM SIGGRAPH, pgs. 439-446.
Another technique (disclosed in Edwards P J, Hawkes D J, Hill D L G, Jewell D, Spink R, Strong A, Gleeson M: Augmented reality in the stereo microscope for Otolaryngology and neurosurgical Guidance. Proceedings of MRCAS 95, Baltimore, USA, 1995, pp 8-15) uses an operating microscope as a device for overlaid display of 3D graphics. By “image injection” of stereoscopic structures into the optical channels of the microscope the surgeon sees the superimposed image over the surgical scene. This technique overlays simple meshes with a relatively low resolution onto the surgical scene, without providing any interactive capabilities. The authors report difficulties regarding the stereoscopic perception of the overlaid data in relation to the real view.
Although meant for guidance of the user, these techniques are all limited in application and usability.